Heat exchanger and method for manufacturing such

ABSTRACT

Heat exchanger comprising at least a heat exchanger space, a burner space and a water conducting channel, wherein the heat exchanger comprises a body having at least one slot and at least one cassette insertable into said at least one slot, said cassette comprising at least part of a water conducting channel.

The invention relates to a heat exchanger and a method for manufacturing such.

Heat exchangers are used in heating apparatus such as central heating heaters, boilers and the like. In such heat exchangers a burner is provided, fired by for example gas or oil. Heat generated by the flames extending from the burner is exchanged between heated gas and heat exchanging surface of the heat exchanger, from which it is in turn transferred to a fluidum provided in channels or spaces within the heat exchanger, such as water for central heating, air or water for household use. In such heat exchangers pressure is build up during use, at elevated temperatures. This provides for special requirements with respect to sealing of such heat exchangers. In such heat exchangers especially flow paths for water and heated gasses have to be well defined in order to obtain an optimal heat transfer from the heated gasses to water flowing through the water duct or ducts.

A problem of known methods for manufacturing heat exchangers is that for different capacities, flow resistance or flow paths of or in the heat exchangers different moulds are necessary. This means that large investments are necessary for series of such heat exchangers, for the necessary tooling.

EP2401571 discloses a heat exchanger having a burner space connected to a heat exchanging space and at least one water duct, the water duct being in heat conducting relation to a wall of the heat exchanging space. In this known heat exchanger the water ducts are at least partly extruded with the body of the heat exchanger or at least parts thereof, limiting the freedom for designing these water ducts. Moreover machining of the extruded body or body part may be necessary, whereas side closing elements are necessary for closing of opposite sides of the water duct.

DE102005010508 discloses a heat exchanger comprising two cast part, together enclosing a burner space and a flue gas channel. Water channels extend around the flue gas channel, integrated in the cast parts. Heat exchanging surface increasing elements in the form of pins extending from a front or rear wall, perpendicular to a main direction of flow of gas through the flue gas channel are provided inside the flue gas channel. Each cast part comprises integral partitioning walls extending from a side of the front or rear wall opposite the pins, defining water channel parts. In two side walls water ducts are integrally formed, connecting the water channel parts of the two cast parts, for forming one water channel extending around the flue gas channel. In the direction of flow the water channel has a decreasing cross section. A lid can be placed over the partitioning walls and water channel parts formed there between, for closing off the water channel parts.

WO2010/098666 discloses a heat exchanger comprising at least a heat exchanger space, a burner space and a water conducting channel. The heat exchanger comprises a body having at least one slot separated from the heat exchanger space and/or the burner space by a wall of the slot. In WO2010/098666 several such slots can be provided, each slot forming part of the water conducting channel. Each of these slots has a straight configuration, defined by two parallel walls and two separating walls interconnecting said parallel walls. One of the parallel walls separates the slot from the burner space and/or the heat exchanger space through which flue gas flows during use. Water can flow unobstructed through said slots.

EP0789203 discloses a heat exchanger comprising a series of modules, each having a burner space on a first side of a separating wall and a water channel at an opposite side thereof. Each module is formed as an integral part to be connected to an identical part. At least part of the water is fed from a central inlet pipe directly to the area of the burner space and from there towards a central outlet pipe. At opposite ends of such series of modules lids or end parts will be provided closing off the water channels.

One aim of the present invention can be to provide relatively inexpensive heat exchangers for heating systems, comprising a burner for creating heated flue gasses in the heat exchanger and feeding these into a heating space of said heat exchanger. Another aim can be to provide a method for manufacturing such heat exchangers or parts thereof, which is relatively inexpensive, especially compared to known methods. A still other aim can be to provide a method for manufacturing series of such heat exchangers having different capacities and/or characteristics. At least one of these aims can be achieved by a heat exchanger or a method according to the present invention. These aims are not mentioned in any relevant order or decisive for the present invention over the prior art.

In a first aspect a heat exchanger according to the present description can be defined by comprising at least a heat exchanger space, a burner space and a water conducting channel. The heat exchanger comprises a body having at least one slot and at least one cassette insertable into said at least one slot, said cassette comprising at least part of a water conducting channel.

In another aspect a method according to the present description can be defined by a method for manufacturing a heat exchanger or parts thereof comprising the steps of:

-   -   forming a heat exchanger body provided with at least part of a         heat conducting space and a slot extending in a first direction         of said body;     -   forming at least one cassette provided with a water conducting         channel part;     -   inserting the at least one cassette into said at least one slot,         forming a water conducting channel through said body, preferably         between two opposite ends thereof.         These steps do not have to be performed in this order.

In embodiments at least two parts for forming at least part of the body are extruded or cast. The parts can then for example subsequently be connected, for example elastically bonded to each other for forming a fluid space. If any part is extruded, preferably between extruding and bonding the parts at least one of the parts is machined by removing at least part of heat exchanging surface enhancing elements integrally extruded in the parts, for forming at least part of a burner space and/or a part of a heat exchanging space.

From EP1707896 an auxiliary heat exchanger is known, comprising a box shaped part 10 comprising a water channel, extending between an inlet and a directly adjacent outlet. The box shaped part has two opposite, parallel closed side walls having a relatively large surface area compared to the thickness of the box shaped part between said side walls. The auxiliary heat exchanger further comprises an outer casing 11, again substantially box shaped, with two parallel side surfaces, a top and bottom surface and a rear surface. A side opposite the rear surface is substantially open. Baffles extend from an interior side of the side surfaces for forming flue gas channel parts. Between facing edges of the baffles extending from opposite side surfaces a space is left, such that the outer casing can be fit over the box shaped part 10 comprising the water channel. A flue gas inlet and flue gas outlet are provided on the top surface. A lid can be connected to the box shaped part 10 for closing the front side of the outer casing when the box shaped part is positioned between said baffles. The said free edges of the baffles are said to be close to the side surfaces of the box shaped part.

During use the inlet of the water channel is connected to an outlet end of a heating circuit, whereas the outlet of the water channel is connected to an inlet of a water channel in a heating boiler having a burner. The flue duct is connected between a flue gas outlet of said heating boiler and a chimney. Thus flue gas cooled inside the heating boiler can be cooled further in the auxiliary heat exchanger of EP1707896, by pre-heating water flowing from a heating circuit prior to feeding it to the heating boiler. Since the space within the outer casing is provided between the free edges of the baffles, the space in the outer casing is entirely open once the outer casing has been removed from the box shaped part comprising the water channel. Thus the flue gas channel in the outer casing and the outside of the box shaped part can easily be cleaned, whereas the outer casing can easily be removed without having to disconnect the water channel from the heating circuit and heating boiler. The auxiliary heat exchanger of EP1707896 does not have a burner and is operated at relatively low temperatures for the flue gasses and water flowing through it compared to a heat exchanger of a heating boiler with a burner as known from e.g. WO2010/098666 or EP0789203.

The present invention shall be further elucidated in the following description, with reference to the drawings, in which:

FIG. 1 shows a heat exchanger, schematically, in perspective view;

FIG. 2 in perspective view a part of a heat exchanger, shown generally from a first side;

FIG. 3 in perspective view a part of a heat exchanger, shown generally from an opposite side;

FIG. 4 a partly assembled heat exchanger from a first end;

FIG. 5 a first part of a heat exchanger in a side view;

FIG. 6 a second part of a heat exchanger in a side view;

FIG. 7 in perspective view a partly assembled heat exchanger from a second side;

FIG. 8 a heat exchanger of FIG. 7, with a mounted end plate;

FIG. 9 a heat exchanger of FIGS. 7 and 8, from an opposite end;

FIG. 10 schematically a gas flow path of a heat exchanger according to the present disclosure;

FIG. 11 schematically a water flow path of a heat exchanger according to the present disclosure;

FIG. 12 in perspective view schematically and enlarged part of a heat exchanger part;

FIGS. 13A and B in frontal and side view a part of a heat exchanger part, in further detail;

FIGS. 14A and B in side view connecting parts of a heat exchanger part, in further detail

FIG. 15 in perspective view a heat exchanger, partly open and with a cassette partly inserted into the heat exchanger;

FIG. 16 in perspective view a heat exchanger, with a cassette partly inserted into the heat exchanger; and

FIG. 17 schematically a cassette for inserting into a heat exchanger.

In this description different embodiments of heat exchangers and parts thereof, as well as heating circuits equipped therewith are disclosed and described by way of example only. In these embodiments the same or similar parts have the same or similar reference signs. Combinations of parts of the embodiments shown are also considered to have been disclosed herein. In this description a heat exchanger has to be understood as an exchanger for exchanging heat between heated flue gasses from a burner and water flowing through one or more water channels within said heat exchanger. Preferably a burner space is provided into which a burner can be inserted, such that said heated flue gasses are actively created, during use, within said heat exchanger. In an alternative the burner can be at least partly integrated in the heat exchanger, for example by extrusion, casting and/or machining. Such heat exchangers are especially, but not exclusively suitable in domestic and commercial heating systems such as boilers and central heating systems, such as for space heating and/or tap water heating systems.

In the following description extrusion, possibly combined with machining of extruded parts, shall be described as an advantageous means for manufacturing parts of such heat exchanger. Nevertheless, some or all of these parts can also be made by casting, such as but not limited to injection moulding, sand or otherwise lost core moulding or casting or the like, possibly combined with machining, such as but not limited to grinding, turning, milling, drilling and the like known machining methods. Parts of heat exchangers according to this disclosure can be made differently, for example by pressing, setting, folding, welding or any other suitable means known to skilled person.

In this disclosure embodiments of heat exchangers shall be disclosed by way of example only. In general terms an element of the present disclosure is that in a heat exchanger for exchanging heat between flue gas and a second medium, preferably a to be heated medium, such as but not limited to water, at least part of a water conducting channel is enclosed in or formed by a cassette, which can be placed inside a slot in a heat exchanger body. The heat exchanger body can in embodiments be made at least partly by extrusion, such that the at least one sot into which a cassette can be provided can be formed during such extrusion. However, also other embodiments can be provided for example cast heat exchanger bodies, or slots extending in different directions. Slots can be open or closed, can be single or multiple in a heat exchanger, and slots can be provided for receiving a single cassette or several such cassettes.

In this disclosure a cassette is to be understood at least as meaning an element insertable into slot in a heat exchanger. A cassette can be closed except for an inlet and outlet, or can be open at at least one side, such that for example at least part of a wall of the slot into which it is inserted and/or part of another such cassette can close said cassette or at least part of a fluid duct, especially a water duct enclosed therein and/or formed thereby. Closed off has to be understood as at least including meaning closing it such that the fluid channel or duct is fully enclosed within the cassette, substantially only fluidly communicating with the environment of the cassette through one or more inlets and one or more outlets of the channel or duct.

In FIG. 1 schematically a heat exchanger 1 is shown, in perspective view, generally from a second side. This heat exchanger 1 comprises a first part 2, a second part 3, a first end part 4 and a second end part 5. In a heat exchanger 1 according to this description at least one of the first and second parts 2, 3 and/or the first and second end parts 4, 5 can be made at least partly by extrusion. At least one of these parts 2, 3, 4, 5 is preferably made of light metal, such as aluminium, aluminium alloy, magnesium, magnesium alloy, or other metal. Preferably all parts 2, 3, 4, 5 are made at least partly by extrusion and at least partly of metal, preferably light metal.

In the embodiments shown at least two of the first 2 and second part 3 and the first 4 and second end part 5 can be mutually connected together for forming at least one of a gas flow space 6 and a water flow space 7. The gas space 6 and water flow space 7 can for example comprise one or more channels. In the embodiment of FIG. 1 the second end part 5 comprises a first and second channel part 8A, 8B, both having a length direction L₈. The length directions L₈ are in this embodiment parallel, such that the end part 5 can be extruded in the length direction L₈. In each of the channel parts 8A, 8B an opening 9A, 9B is provided, for example by drilling. Screw treads can be provided in the openings 9A, 9B in order to connect piping to these openings, as will be discussed later on. The parts can be connected mutually by bonding or welding. Alternatively and/or additionally the parts can be interconnected mechanically for example by screws, bolts, clamps, press fittings or the like means, in which case at least preferably appropriate seals are used.

In this description bonding has to be understood as forming an adhesive connection between two or more parts using an elastic bonding agent. Especially suitable is a glue or adhesive which after curing is still flexible and elastically deformable. Preferably the bonding agent is heat resistant to temperatures above 120° C., preferably above 150° C., more preferably above 170° C. A glue can be used having a temperature resistance up to 180° C. or above. A glue can be used having a use temperature range between about −4 and +120° C., preferably between about −20 and +150° C., more preferably between about −40 and +170° C., even more preferably between at least −55 and 180° C. or higher (e.g. PSI S406). A temperature range should be understood as a range of temperatures in which the glue maintains at least most of its elastic and bonding properties, such that in a heat exchanger at least the bonding maintains pressure resistant and fluid and gas tight. Pressure resistant is in this context to be understood as at least resistant to pressures in an adjoining space of above 2 bar, preferably above 4 bar, more preferably at least to 10 bar. The desired pressure resistance can be as high as 20 bar or above. One bar is 100.000 Pascal or 0.1 MPa. Reference can be made to adhesion to peel, according to ASTM C794.

Elastic bonding agent, such as glue or adhesive should be understood as an agent which, after curing, has during use, a high yield strength and high yield limit. This means it can be stretched to a relatively high degree before breaking. The elasticity is preferably such that the yield limit is more than about 300%, preferably more than about 400%, more preferably more than about 550% and in particular preferably about 650% or more. Preferably this high yield limit is maintained over the temperature range during use of the heat exchanger. The yield limit can e.g. be measured according to ASTM D412.

The bonding agent can be a silicone or elastomeric based adhesive, preferably curing at about room temperature to a rubber like component which is water and gas tight. A bonding layer formed by said bonding agent is preferably pressure resistant to at least about 4 Bar, more preferably to about 10 Bar and even more preferably to about 20 Bar or above, wherein the bonding agent is preferably applied to unprimed metal of the parts. An example of such bonding agent is Dow Corning 7091, which has a normal temperature range of use between −55 and +180° C., and a yield limit of about 680%.

All kinds of combinations can be contemplated of yield limit, pressure resistance and temperature range.

Dow Corning® 7091 Adhesive/Sealant is a high-performance, neutral-cure silicone that cures at room temperature to a tough, flexible rubber, suitable for the use described herein. Dow Corning 7091 remains flexible and stable from −55° to 180° C. (−67° to 356° F.), and is a one-component, non-sag sealant. It can have a tear strength of 86 ppi and a tensile strength of about 363 psi. This adhesive is only provided by way of example and should not be considered limiting the scope in any way.

By using such a flexible bonding agent parts of the heat exchanger can be connected to each other, forming fluid, especially water, and gas tight seals without having to add gaskets, seals or the like, which will remain fluid and gas tight over a large temperature range. Moreover, such seals are relatively inexpensive and are pressure resistant to relatively high pressures. Furthermore, due to the high flexibility, problems with different expansion rates and directions of the different parts bonded together are avoided.

FIG. 2 shown in perspective view a first part 2. This part 2 can be made substantially be extrusion. The part 2 shows a first wall 10 and two second walls 11A, B. The first wall 10 is a substantially hollow wall, defined by a first wall part 10A and a second wall part 10B, for example extending substantially parallel to each other, whereas a number of cross walls 12 extend between the first and second wall parts 10A, 10B. Between the walls 10A, 10B and the walls 12 a series of slots 60 is formed. In this embodiment the slots 60 are open to two longitudinal ends 61A, 61B and extend parallel to each other, preferably in an extrusion direction of the part 2.

The second walls 11A, B extend at an angle α to the first wall 10. The angle α differs from 180 degrees. The angle α is for example between 45 and 135 degrees and is preferably about 90 degrees. The walls 11A, B extend in a first direction from the first wall 10. One or more of the second walls 11A can be lower than at least one other wall 11B of the second walls 11. On the first side of the first wall 10 an intermediate wall 13 extends, in the same direction as the second walls 11. Between each of the second walls 11A, B and the intermediate wall 13 a series of fins 14 is provided, extending in the same first direction from the first wall 10. The fins 14 can form heat exchanging surface increasing elements. As shown in FIG. 2 the second walls 11, the intermediate wall 13, the cross walls 12 and the fins 14 all have a length direction X and thus extend substantially parallel to each other. The free ends 15 of the second walls 11 and the intermediate wall 13 can have a groove 16 extending in the said length direction X, open to a side facing away from the first wall 10.

As is shown in FIG. 2 to the right side of the intermediate wall 13 the fins 14 can have a reclining end 17, such that the fins 14 have a greater length XA near the first wall 10 than the length XB at the opposite free side 15 thereof. The opposite end 18 of the fins can be straight, such that the second ends 18 of the fins 14 form a substantially flat plane V extending substantially perpendicular to the first wall 10, for example at a distance B from the opposite edge 20. These fins 14 can end at a distance A from the edge 19 of the first wall 10. The intermediate wall 13 extends from the edge 19 to a distance B from the opposite edge 20 of the first wall 10. The reclining ends 17 can in an alternative also be e.g. convex or concave. The space created thereby can be narrowing in the direction of the edge 20. Obviously the reclining ends can also be substantially or partly convex of concave or have another regular or irregular shape, providing said effect of a narrowing burner chamber 30

As is shown in FIG. 2 to the left side of the intermediate wall 13 the fins 14 can have a straight end 21, such that the fins 14 have about the same length XC near the first wall 10 as at the opposite free side 15 thereof. The opposite end 22 of the fins can be straight, such that the second ends 22 of the fins 14 abut the same substantially flat plane V extending substantially perpendicular to the first wall 10. Some of the fins 14, positioned next to the intermediate wall 13 can end at a distance C from the edge 19 of the first wall 10. The further fins 14 can extend the full length X of the first wall 10.

At two opposite outer sides of the second walls 11A, B a profile 23 is provided, having a substantially circular inner cross section. At the base of the intermediate wall 13 a further opening 23A can be provided, extending all the way through the relevant part 2, 3.

This first part 2 can be made by extruding a continuous length of profile having a cross section as for example shown in FIG. 5. A desired length X₁ can be sawn off from the continuous length. Then part of the first ends 17 of the fins 14 can be removed, for example milled or sawn off, as can the second end of the intermediate wall 13. Because of the open side of the parts this is easily accessible for such machining. In the embodiment shown five cross walls 12 are shown, dividing the space 24 within the double first wall 10 into four parallel channel parts 24A, 24B, 24C, 24D forming essentially the slots 60. Different numbers of channels or slots 60 can be used. The two middle channel parts 24B, C are connected to each other by removing part of the first end 25 of the cross wall 12 in between, whereas the left hand two channel parts 24A, 24B in FIG. 2 are connected to each other by removing part of the second end 26 of the intermediate cross wall 12, adjacent the plane V. In a similar manner part of the second end 26 of the cross wall 12 between the right hand two channel parts 24C, 24D can be removed to connect these two channel parts 24C, 24D. Inside the slots 60 formed by the channel parts 24 cassettes 62 can extend which form part of a water conducting channel 6 as will be further discussed.

FIG. 3 shows the first part 2 as shown in FIG. 2, from the opposite second side. Here clearly the second ends of the fins 14 and the second walls 11 and intermediate wall 13 can be clearly seen, forming a plane Ve, parallel to the plane V. Planes V and Ve are imaginary planes.

Between the fins 14 and between the walls 11, 13 and adjacent fins 14 spaces are provided, such that a substantially regular pattern can be formed. The second part 3 can be formed in a similar way.

In embodiments at the free ends of the walls 10 and 11, at opposite ends seen in the length direction X_(C), bonding surfaces B₁ and B₂ respectively can be formed. These bonding surfaces are preferably flat and even. As is schematically shown in e.g. FIGS. 3-7 and further and in larger detail shown in FIGS. 12 and 13, these bonding surfaces can be provided with spacer elements 52. These spacer elements 52 can be integral part of the parts 2 and/or 3 and/or of end parts 4 and/or 5. The spacer elements can be small elevations above the bonding surfaces B, which can be provided by machining of said surfaces B, for example milling. In another embodiment these spacer elements 52 can be provided in or on the surface separately and e.g. be glued or screwed in place. The spacer element extent to a relatively short distance d₁ above said bonding surface B, for defining a thickness t₁ of the bonding layer 53, as is shown in FIG. 13B. In FIG. 12 a perspective view of a part of a first or second part 2, 3 or of an end part 4, 5 is shown, in enlarged view, showing a substantially cylindrical spacer element 52. Obviously these spacer elements 52 can have any desired shape or form, and a height d₁ depending on the desired, optimal thickness t₁.

In FIG. 14A shows in side view a ridge 27 on a wall 11, 13 of a second part, by way of example only, whereas to the side of said ridge 27 shoulders 54 are formed, as part of the wall 11, 13 having a larger width than the ridge 27. On each shoulder, or on only one if desired, at least one spacer element 52 is provided, again having a relatively low height d₁ above the surface of the shoulder 54. This can for example be a ridge extending over a length of said wall 11, 13, or one or more shorter elements, such as for example pins, ribs or the like. In FIG. 14B such spacer elements 52 are shown on the end surface of the wall 11, to the sides of the groove 16. Again the height d₁ is relatively small. Similar elements can be provided on top of the ridge 27, to the sides thereof and/or at the bottom 56 of the groove 16. In FIG. 14 B the bonding layer 55 is sketched in by phantom lines, as an indication. Preferably the space between the ridge 27 and the inner wall of the groove 16 has a width t₁ similar to the height d₁ of the spacer elements 52. The

The spacer elements 52 have the advantage that they define the minimum space between two opposite bonding surfaces B of for example the first and second parts 2, 3 and/or the end parts 4, 5, thus defining the thickness t of the layer of bonding agent, and more specifically defining an even thickness thereof over the entire relevant surface B, or between the ridge 27 and the groove 16 cooperating therewith. This means that the optimal amount of glue can be used, reducing costs, whereas the best bonding and sealing can be obtained easily with the relevant bonding agent. This is obtained by at least one bonding surface B abutting the spacer elements 52 on the at least one other bonding surface it is to be bonded with, preventing it from being pressed closer to said bonding surface. The height of the spacer elements 52 above the relevant bonding surface B can be in the order of tenth's of millimetres or less, e.g. between 0.01 and 1.5 mm, preferably less than 1 mm. Obviously the height and thus the thickness of the layer can be chosen dependent on the characteristics of the bonding agent used, for optimisation. By minimizing the thickness of the layer of bonding agent 55, the transfer of heat between the parts bonded together will be maintained. Moreover, due to the fact that one of the parts will be in direct contact with the or each other part it is bonded to by the abutting contact between the bonding surface of one of said parts with spacer elements on another bonding surface it is bonded too, there will be direct metal to metal transfer of heat, which will further optimize the heat transfer.

In FIG. 4 a partly assembled heat exchanger 1 is shown, in side view, in which at least a first 2 and second part 3 are shown, assembled. In FIGS. 5 and 6 respectively the first part 2 and the second part 3 are shown, equally in side view. As can be seen the second part 3 has a cross section similar to that of the first part, but the second walls 11C, 11D and the intermediate wall 13B have heights such that when positioned on the second walls 11A, 11B and 13 respectively, the first wall 10 of the first part 2 extends parallel to the first part 10 of the second part 3, thus forming a substantially rectangular cross section. The second walls 11C, 11B and the intermediate wall 13 of the second part 3 have ridges 27 that can fit in the grooves 16. The fins 14 of the first part 2 can extend between the fins 14 of the second part and/or between a fin and either a second wall 11C, D or the intermediate wall 13 of the second part. The fins 14 can have a substantially triangular or trapezoid cross section with a base 28 near the respective first wall 10 broader than the free side thereof.

As can be seen the channel parts 24 of the first walls 10 can have a ribbed or otherwise corrugated or channelled surface, at least at the side of the fins 14, in order to increase the heat exchanging surface of the channel parts 24. In other embodiments these sides of the channel parts 24 can be flat, that is without such ribs. Heat of the fins 14 can be transferred to water in the cassettes 62 inserted in the channel parts 24 through the first wall 10.

The first part 2 is bonded to the second part 3, by bonding the second walls 11A, B of the first part 2 to the second walls 11C, D of the second parts 3. The intermediate wall 13 of the first part 2 can also be bonded to the intermediate wall 13 of the second part 3. Preferably at least the ridges 27 can be bonded in the grooves 16. Bonding can be achieved by glue, for example acrylic glue, two or more component glue, PLEXUS MA 420, PERMABOND ES 550 or DOW CORNING 7091. As can be seen in FIG. 4 preferably the grooves can have an open side having a width slightly less than the adjacent part of the groove 16, whereas the ridge 27 can have a width substantially similar to the width of the open side. This means that glue in the groove 16 will be locked in the groove by forcing the ridge 27 into the groove 16, whereas the ridge 27 will be centred within the groove 16, when the opening is provided symmetrically. The space between the ridge 27 and the walls of the groove 16 is preferably similar in width to the height of the spacer elements 52, such that a layer of bonding agent can be formed between said ridge 27 and groove 16 similar in thickness as that between the bonding surfaces as discussed before.

When an embodiment of a ridge 27 and/or groove 16 is used as disclosed in FIGS. 14A and B, spacer elements 52 can again be used for defining the thickness of a layer of bonding agent.

As can be seen in the various figures, the spacer elements 52 can be distributed over all or some of the bonding surfaces B and/or end parts 4, 5. Preferably they can at least be provided on first walls 10 near partition walls 12 and near walls 11 and 13, as well as on the walls 11 and 13. Moreover they can be provided for example at feet 50. Preferably they are distributed such that pressure applied to the parts and, especially, the parts 4, 5 does not significantly bend or otherwise deform any surface in between the spacer elements 52. The spacer elements 52 are preferably provided at a short distance from a or, more preferably, at a distance from each of the sides of the relevant bonding surface they are provided on. This has the advantage that the bonding agent can surround the spacer element 52 at least partly within the layer of bonding material, or at least form a continuous seal between the bonding surfaces B alongside the spacer elements, and preferably can surround the spacer elements 52 entirely, for forming both a good adhesion between the bonded parts and a good sealing. Again, the direct contact between the metal parts through the spacer elements will improve the heat transfer between parts. The relatively small thickness of the bonding layer 55 will furthermore prevent thermal isolation further. Moreover this prevents too flexible seals.

FIG. 7 shows a partly assembled heat exchanger 1, open at the first side, showing the second walls 11A, C and 11B, D bonded to each other, as well as the intermediate walls 13. Between the first walls 10 and the second walls 11 of the first and second parts 2, 3 a heat exchanging space 30 is defined, at least partly. At two opposite sides of the space 30 in the respective first wall 10 at least one cassette 62 and preferably a series of cassettes 62 is provided in the channel parts 24 for forming part of a duct 6 for e.g. water. A second end part 5 is partly visible at the second side of the heat exchanger 1. At the first side the fins 14 are visible. At one side of the intermediate walls 13 the reclining ends 17 of the fins 14 are shown. Between the edge 19 and the ends 17 of the fins 14 a burner space 31 is provided. In the burner space 31 a burner can extend at least partly or, when a burner is used which is provided outside said space 31, then flames can extend into the space. The reclining ends 17 are provided to prevent undesired tension in the fins 17. At the opposite side of the intermediate walls 13 a space 32 can be provided, in order to reduce flow resistance and improve the heat exchange between heated gas flowing through the space 30 between the fins 14 and/or the fins and the walls 11, 13.

In FIG. 8 a heat exchanger 1 is shown, similarly to FIG. 7, but with a first end part 4 at the first side of the heat exchanger 1. The first end part 4 can be bonded, such as glued to the first and second parts 2, 3. Similarly the second end part 5 can be bonded, such as glued to the second side of the heat exchanger 1. Again spacer elements 52 can be used for defining the optimal or at least desired thickness of the layer of bonding agent. In the first end part 5 a first opening 33 is provided, opening into the burner space 31. A second opening 34 is provided, opening into the space 32. In and/or over the first opening 33 a burner 34 can be positioned, as is shown in FIG. 10. In and/or over the second opening a gas exhaust 35 can be connected, as is shown in FIG. 10.

As can be seen in FIGS. 8 and 9 in an embodiment the channels 8A, B can extend beyond the periphery of the first and second parts 2, 3. In the embodiment of FIGS. 8 and 9 the channels parts 8A, b extend in opposite directions beyond the periphery. In each of the extending portions 35A, 35B an opening 9 is provided, for example by drilling or milling, preferably provided with internal screw threads or another means for attaching a pipe of a heating circuit. An inlet of a heating circuit can be connected to one of the openings 9, an outlet of the heating circuit to the other opening 9. The openings 9 are preferably provided in a wall 38 of the channels facing in the direction of the first and second part 2, 3 of the heat exchanger 1. This can provide a compact heat exchanger and easy access. The open ends 36 of the channels parts 8A, B can be closed off by stops 37, as is shown in FIG. 1. The stops can also be bonded such as glued. In the wall 38 of each of the channel parts 8A, B at least one further opening 51 is provided, opening into a channel part 24 inside a first wall 10, for fluidly connecting the channel part 24 with the channel part 8 and thus with the relevant opening 9. In the embodiments of FIGS. 1 and 8 one channel part 8A is connected to a first channel part 24A, and thus to a cassette 62 inserted into such channel part 24A of each of the first walls 10, whereas the other channel part 8B is connected to the last channel part 24D, and thus to a cassette 62 inserted into such channel part 24D of the first wall. In the embodiments shown this is the fourth channel part 24D but obviously other numbers of channel parts can be provided, whereas the channel parts 8A, B or further such channel parts 8 can be connected to other channel parts 24 or even to each of the channel parts 24, and/or to cassettes 62 provided therein, depending on the desired flow paths of the water through the walls 10.

The first and/or second end parts 4, 5 can basically be made by extrusion, the extrusion direction in the length direction L₈ of the channel parts 8A, B. For an embodiment of for example FIGS. 8 and 9 parts of the wall 38 can be removed, for example by milling or sawing, to provide for the extending portions 35A, B. Openings 9 can be provided then by for example drilling or milling. The end parts can be bonded, such as glued, to the first and second parts 2, 3. The end parts 4, 5 can be provided with further openings 39. When assembling the heat exchanger bolts or rod with ends provided with screw threads can be inserted through these openings 39 and the channels 23 or openings 23A extending there behind, after which nuts can be screwed onto the bolts or screw thread of the rods, in order to further clamp the end parts 4, 5 to the first and second parts 2, 3. This can provide for further mechanical strength.

In FIG. 10 schematically a gas flow path is shown, thorough the inner space 30 of a heat exchanger 1, between the burner 34 and the exhaust 35. As can be seen gas, heated by the burner 34 can flow, as indicated by arrows G from the burner space 31 in which part of the burner 34 extends and during use flames are provided by the burner 34, into the spaces between the fins 14 and/or fins and adjacent walls 11, 13. At the second side opposite the burner 34 the gas can flow between the end part 5 and the end 19 of the intermediate wall 13, in to the spaces between the fins 14 in the space between the second end part 5 and the exhaust 35. From there the gasses can flow into the exhaust 35 to be expelled. A condensate drain 40 can be provided in or next to the exhaust 35.

As can be seen in FIG. 10 in this embodiment the length of the fins 14 in the space between the second end part 5 and the exhaust can vary, such that the fins closest to the intermediate wall 13 are longer then fins closer to the second wall 11B and the space 32 has a substantially trapezoid shape. This has the advantage that all gasses flowing through the space 30 have about the same contact with fins, independent of their flow path.

In FIG. 11 schematically a water flow path is shown through the first walls 10 and the channel parts 8A, B. In this embodiment water is provided to the heat exchanger 1 through an inlet 41 into the channel part 8A. The inlet 41 is shown as a pipe 42 extending from a heating circuit 43, schematically shown in FIG. 11 as having a pump 44 and a radiator 45, and connected to the relevant opening 9. In other embodiments this can for example be a household water or sanitary water supply, a boiler, or other means using heated water or other heated fluids or gasses. The water flowing from the inlet 41 flows into the channel part 8A and is divided over both channels 24, and thus cassettes 62 in the respective first and second part 2, 3. In FIG. 11 only one of these channels 24 formed by or at least containing the slots 60 housing the cassettes 62 is shown. The water then flows through the cassettes 62 provided in the channel parts 24 A-D, to the other 8B of the two channel parts 8 as is shown by arrows W, through which the water from both channels 24 and the cassettes 62 provided therein can flow into an outlet 45, here shown as a pipe 46 connected to the heating circuit 43. Thus heat can be exchanged between the gasses flowing through the space 30 and the fins and walls, especially walls 13 and 10, which heat can then be transferred to water or other medium flowing through the channels 24 and especially the cassettes 62 therein, to be used in the heating circuit 43. The flow through the channels 24 and especially the cassettes 62 and the space 30 if preferably such that water and gas have counter flow directions as much as possible. This can for example be obtained by positioning the inlet 41 in the second end part 5 at the exhaust 35 side of the intermediate wall 13, the outlet 45 being provided on the opposite side of the intermediate wall 13, in the second end part 5.

Obviously in FIG. 11 the arrows W indicate a general direction of flow of water through a relevant slot, whereas the actual flow of water may be defined by the partitioning walls 67, defining a zig-zag or meandering flow path for the water through one, some or all of the slots. The slots are formed as spaces separated from the flue gas channel by a common wall integral to the body of the heat exchanger, such that the slot itself can define a water channel part and/or a cassette inserted therein. Moreover, the or each slot enclosed in a wall of a heat exchanger part has the advantage that even if the heat exchanger part may expand slightly, due to the relatively high temperatures, the slot will remain being separated form the flue gas channel and burner space, whereas the flue gas channel and burner space also remain closed to the surrounding, the flow path of the flue gas remaining well defined.

As will be understood the bonding agent such as glue used for bonding different parts of the heat exchanger 1 to each other preferably provides a sealing between these parts too, which provides for a water and gas tight connection without the necessity of further sealing means such as seals. In other embodiments sealing of at least some of the parts relative to each other can be obtained through other means, such as seals, gaskets or the like sealing means. By using an elastic bonding agent for connecting and sealing parts of the heat exchanger, the surprising advantage is obtained of lower cost, and better sealing than when a hard or hardening agent is used. Moreover, due to the bonding, especially in combination with spacer elements, the connection can be made strong and gas and fluid tight, as well as pressure resistant.

A heat exchanger 1 according to the present invention is relatively easy to produce, is economical in comparison to heat exchangers having the same capacity made by for example moulding or welding, and can easily be adapted for example different capacities, set up such as amendment of the position of the inlet and/or outlet 41, 45, the burner 34 and the layout of the channels 24 and fins 14. Moreover, a range of heat exchangers 1 can be provided, differing basically only in the length X₁ of the first and second part 2, 3. These different heat exchangers will have different capacities, depending on and mainly in relation to the length X₁. This means that with the same extrusion tools different heat exchangers can be made, reducing production costs. Moreover, by using cassettes 62 as disclosed for example in FIGS. 11 and 15-17 the flow of water through the water duct 6 can be easily and more freely be defined, for example based on a desired flow, water resistance, time of presence of water inside the water duct 6 and the like. By using a cassette or a series of cassettes 62 having a longitudinal direction Lc, for example extending substantially between a first side 61A comprising an inlet 64 and a second side 61B comprising an outlet 66, and cross walls 67 extending non-parallel to said longitudinal direction Lc, a flow W through the cassettes 62 can be obtained which is also substantially non-parallel to said longitudinal direction Lc, and can for example be for example zigzag, passed the cross walls 67. Instead of or supplementary to said cross walls 67 also other heat exchanging surface increasing elements could be provided in said cassette, such as for example ribs, notches, pins, pens, flow restrictions or any such flow interfering elements as known in the art, especially including such elements which cannot be extrude with the slots 60. The cassettes and/or said elements can be made of the same or different materials than the parts 2, 3.

The first and/or second part 2, 3 can be provided with flanges 50 for supporting the heat exchanger.

FIGS. 15 and 16 show schematically a heat exchanger or part thereof, comprising at least one slot 60 within a wall 10 of heat exchanger body 70, for example but not necessarily formed by parts 2, 3 as discussed before. In the embodiment of FIG. 15 there are shown two slots 60 in a wall 10, each receiving a cassette 62 comprising a part 6A of a water duct 6, one having been fully inserted. In this embodiment the cassettes 62 comprise a first wall 68 for engaging a wall of said at least one slot 60, for example wall 10A or 10B, and a labyrinth forming wall or wall complex extending from said first wall 68, defining said part 6A of a duct 6. The part 6A extends between an inlet side 61A and an outlet side 61B of the cassette 62. In the embodiment shown the labyrinth forming wall complex comprises two side walls 69 extending along opposite longitudinal sides of the first wall 68 and cross walls 67, connected to the first wall 68 and alternatingly extending from one of the side walls 69 towards the opposite side wall 69 but stopping short from it to leave a relatively small gap 71. Thus a zig-zag path is obtained forming the part 6A.

FIG. 17 shows a cassette 62 for use in a heat exchanger 1, for example as previously disclosed. This heat exchanger can for example be made of metal sheet material, for example steel, aluminium, magnesium or metal alloys, such as but not limited to light metal alloys. It can be made in any suitable way, for example by setting drafting, pressing, casting or the like methods, known to the skilled person. In the embodiment shown the cassette 62 is open at a side opposite the first wall 68, but that side can also be partly or entirely closed, for example by a second wall, which can be mounted to the side walls 69 and/or cross walls 67. In another embodiment cassettes 62 can be placed on top of each other, the one closing off the open side of the other and possibly vice versa. When using a cassette 62 which is open at one side, opposite the first wall 68, a wall 10A, 10B of the slot 60 will close off the cassette 62 or at least the part 6A of the water duct 6 therein.

In FIGS. 11 and 15 to 17 the water channel part 6A extends zig-zag along the walls 67, between inlet 64 and outlet 66, wherein the distance 71 between adjacent walls extending from the same side wall 69 decreases from the inlet 64 to the outlet 66, such that the cross section of the flow channel 6A decreases in that direction. By varying for example the distances 71 and thus the shape of the channel part 6A in the cassette 62 or cassettes 62 the flow through the channel 6 can be amended, even without changing the further heat exchanger.

By using one or more cassettes 62, especially cassettes 62 which are open to at least one side, such that it can be made by for example machining or moulding, such as injection moulding or fixed core moulding, in a heat exchanger, such heat exchanger can be more easily made with an appropriate water channel 6. Even if such heat exchanger is made using a heat exchanger body made by moulding, no lost core is necessary for forming the water channel 6. A cassette 62 f this disclosure can be a retarder for keeping the water longer inside the heat exchanger body than when straight channels 24 are used. By using one or more cassettes 62 in a heat exchanger defining the water flow the delta T (ΔT) can be set easily per heat exchanger 1, without the necessity for changing the further heat exchanger body. The water channel 6, or at least the part 6A thereof within the cassette 62 can be made more accurate, thus ensuring an accurate flow and heat exchanging within the heat exchanger body 70. By using one or more cassettes 62 made outside the heat exchanger body 70 no debris resulting from the manufacturing of the water channel will remain and have to be removed from the heat exchanger body 70.

In preferred embodiments the burner 34 can be a burner having a burner deck 47 made using fiber technology. An example of such material is a material referred to as nit in the relevant fields, for example as used and supplied Bekaert Combustion Technology BV, Assen, The Netherlands. A burner range available using such technology is known as Furinit® or Aconit®, trademarks used by Bekaert Combustion Technology BV, Assen, The Netherlands. These burners 34 preferably are premix burners, and can be modulating burners. The fibers can be metal or ceramics or combinations thereof. A burner 34 for use in the present description can be for example a burner having a cylindrical burner deck, a flat or curved burner deck or a dome shaped burner deck, or any other suitable shape an dimensions suitable for the relevant heat exchanger. Burners using fiber technology for the burner deck have at least the advantage that they are compact and still have a relatively large burning surface area, due to the fibers. The burners can be modulated over a very large range, for example but not limited to between 1 and 80 kW/dm² or 1-22 kW/dm². The heat exchanger can be very compact, in relation to the capacity, which renders the use of a compact burner advantageous.

A heat exchanger 1 according to this description can be used as a “stand alone” heat exchanger, for supplying heated medium such as water. In another embodiment the heat exchanger can be used as a “add on” heat exchanger, for example coupled to other heating or power generating means, such as heating devices using “green” energy, electrics, natural gas or the like. Also a number of these heat exchangers can be connected, such that depending on heat demand one or more of these heat exchangers can be fired up to provide heat.

The invention is by no means limited to the embodiments as shown and/or described in this description. Many variations thereof are possible within the scope of the claims, including at least all combinations of parts and elements of the embodiments and parts thereof shown, in any combination or permutation. For example one or both of the walls 10 can be made having separate channel parts above or next to each other for connecting to separate water or other medium circuits. Moreover the first and/or second parts can have other cross sections and can for example have reclining second walls, for providing a larger space 30. The parts can be attached to each other using different means, such as screws, fasteners, clamps, welds or the like. Also other bonding agents can be used, for example two or more component agents. Moreover, the even thickness of the bonding layers and heat conducting properties through the connection thus formed can be achieved in another way, for example by gluing tools and moulds used for exact positioning of the parts during bonding, and/or by providing heat conducting elements connected to both parts, such as but not limited to pins, strips or similar, preferably metal elements inserted in between the bonded parts or to them, crossing said bonding connection. In other embodiments a first part 2 can be used having second walls 11 and intermediate walls 13 extending from both sides of the first wall 10, as well as fins 14, whereas two second parts 3 can be provided at the two opposite sides of the first part 2, providing a space 30 to each side of the first wall 10 of the first part 2. These spaces 30 and the water channels 24 of the different parts 2, 3 can be used for the same or different heating circuits. Such heat exchanger can be equipped with one or two burners 34. Shapes and dimensions, as well as positions of the different parts can be changed within the scope of the claims as pending. Moreover, more or less channel parts 8, 24 can be provided than shown, whereas more than one intermediate wall can be provided, for example two or more, in each of the first and second parts 2, 3, whereas the channel parts, burner and exhaust can be provided in different positions. For example, the burner can be positioned on and/or in the first end part 4, the exhaust in and/or on the second end part 5 when the number of intermediate walls is even, having an even number of direction changes of the gas flow in the space 30. In embodiments the or at least a slot 60 can be open to a side of the heat exchanger body 70, such that a cassette 62 can be inserted into said slot 601 a direction non-parallel to the longitudinal axis Lc of said cassette 62. A heat exchanger according to the disclosure could be made without a burner space, for example for use as an auxiliary heat exchanger or with an external burner.

In the embodiments shown it is preferred that there will be no entrapment of gas during use. Especially preferable is that there will be no entrapment of air in the water ducts, such as in the cassettes. To this end in embodiments it may be favourable that there is for example a sustainably vertical positioning of the heat exchanger, such that the water inlet and outlet are positioned near or at a lower end of the heat exchanger. In embodiments, especially such embodiments, it may be favourable to have the burner positioned at an upper end of the heat exchanger.

In heat exchangers according to this disclosure in stead of metal, such as light metal or light metal alloys, also plastic can be used, for example but not limited to for the cassettes and parts forming the body or housing of the heat exchanger, such as but not limited to parts forming part of the heat exchanging space and/or the water conducting channel and/or the burner.

These and other alterations and modifications are supposed to be disclosed within the scope of the claims. 

1. Heat exchanger comprising at least a heat exchanger space, a burner space and a water conducting channel, wherein the heat exchanger comprises a body having at least one slot and at least one cassette insertable into said at least one slot, said cassette comprising at least part of a water conducting channel.
 2. Heat exchanger according to claim 1, wherein the at least one cassette comprises a first wall for engaging a wall of said at least one slot and a labyrinth forming wall extending from said first wall, extending between an inlet side and a outlet side of the cassette.
 3. Heat exchanger according to claim 2, wherein the at least one cassette comprises a first wall and the cassette is open at a side opposite the first wall and is preferably machined from a metal element.
 4. Heat exchanger according to claim 1, wherein the cassette comprises a labyrinth which at least partly defines a substantially zig-zag flow path through the cassette, between an inlet and an outlet of said cassette.
 5. Heat exchanger according to claim 1, comprising a series of such cassettes, wherein the at least one slot and the cassettes are designed such that at least two cassettes can be inserted into said slot, preferably in a side by side relationship.
 6. Heat exchanger according to claim 1, wherein the water conducting channel in said cassette extends between an inlet and an outlet and has in the flow direction an increasing cross section.
 7. Heat exchanger according to claim 1, wherein the at least one cassette has been inserted into the at least one slot, wherein the part of the water conducting channel in the cassette is closed at least at one side by a wall of the slot.
 8. Heat exchanger according to claim 1, wherein a series of cassettes is provided, each insertable into said at least one slot, wherein the cassettes comprise different water conducting channel parts.
 9. Heat exchanger according to claim 1, comprising at least two parts made at least partly by extrusion or casting from light metal or light metal alloy and/or plastic, said at least two parts mutually engaging for forming part of the heat exchanging space and/or the water conducting channel, wherein each of said at least two parts comprises part of said heat exchanging space and/or said water conducting channel and wherein the burner space is formed in one of or between said at least two parts, wherein at least one of the parts comprises said at least one slot.
 10. Heat exchanger according to claim 9, wherein said at least two parts are connected by an elastic bonding agent, in particular an elastic glue, forming a bond and a seal, wherein at least the water conducting channel of the heat exchanger is pressure resistant.
 11. Heat exchanger according to claim 1, wherein two end parts are mounted to the body of the heat exchanger, at opposite sides thereof, wherein the end parts are preferably bonded to the said two parts by elastic bonding agent, preferably an elastic glue, at least partly closing off at least the heat exchanging space and/or the water channel, and/or wherein said end parts are preferably made at least partly by extrusion and wherein the at least one slot is provided in the body and is open to at least one and preferably both end parts.
 12. Series of heat exchangers, each according to claim 1, wherein at least two heat exchangers in the series are substantially identical, except for at least one cassette inserted therein.
 13. Heat exchanger comprising at least a heat exchanger space and a water conducting channel, wherein the heat exchanger comprises a body having at least one slot and at least one cassette insertable into said at least one slot, said cassette comprising at least part of a water conducting channel, wherein the at least one slot is enclosed in a wall portion of the heat exchanger, separated from the at least one heat exchanger space.
 14. Heat exchanger according to claim 13, wherein the at least one cassette comprises a first wall for engaging a wall of said at least one slot and elements extending from said first wall.
 15. Heat exchanger according to claim 13, wherein the at least one cassette comprises a first wall and the cassette is open at a side opposite the first wall.
 16. Heat exchanger according to claim 13, wherein the cassette is made using machining.
 17. Heat exchanger according to claim 13, wherein the cassette comprises a labyrinth which at least partly defines a substantially zig-zag flow path through the cassette, between an inlet and an outlet of said cassette.
 18. Heat exchanger according to claim 13, comprising a series of such cassettes, wherein the at least one slot and the cassettes are designed such that at least two cassettes can be inserted into said slot.
 19. Heat exchanger according to claim 18, wherein the cassettes can be inserted into the at least one slot in a side by side relationship.
 20. Heat exchanger according to claim 13, wherein the at least one cassette has been inserted into the at least one slot, wherein the part of the water conducting channel in the cassette is closed at least at one side by a wall of the slot.
 21. Heat exchanger according to claim 13, wherein a series of cassettes is provided, each insertable into said at least one slot, wherein the cassettes comprise different water conducting channel parts.
 22. Heat exchanger according to claim 13, comprising at least two parts made at least partly by extrusion or casting from light metal or light metal alloy and/or plastic, said at least two parts mutually engaging for forming part of the heat exchanging space and/or the water conducting channel, wherein each of said at least two parts comprises part of said heat exchanging space and/or said water conducting channel and wherein the burner space is formed in one of or between said at least two parts, wherein at least one of the parts comprises said at least one slot.
 23. Heat exchanger according to claim 22, wherein said at least two parts are connected by an elastic bonding agent forming a bond and a seal, wherein at least the water conducting channel of the heat exchanger is pressure resistant.
 24. Heat exchanger according to claim 23, wherein the bonding agent is an elastic glue, forming a bond and a seal.
 25. Heat exchanger according to claim 13, wherein two end parts are mounted to the body of the heat exchanger, at opposite sides thereof, wherein the end parts are connected to said two parts, at least partly closing off at least the heat exchanging space and/or the water channel, and/or wherein said end parts are made at least partly by extrusion and wherein the at least one slot is provided in the body and is open to at least one end part.
 26. Heat exchanger according to claim 25, wherein the at least one slot is open to both end parts.
 27. Heat exchanger according to claim 13, wherein further a burner space is provided, part of or connecting to the heat exchanging space in the heat exchanger, separated from the at least one slot.
 28. Method for manufacturing a heat exchanger or parts thereof, comprising the steps of: forming a heat exchanger body provided with at least part of a heat conducting space and a slot extending in a first direction of said body; forming at least one cassette provided with a water conducting channel part; inserting the at least one cassette into said at least one slot, forming a water conducting channel through said body, preferably between two opposite ends thereof.
 29. Method according to claim 28, wherein the body is formed using one or more extruded or cast elements and wherein the at least one cassette is formed by machining metal, such that a cassette is formed having a first wall and channel defining walls extending from said first wall, forming a labyrinth shaped water channel part, open at a side opposite the first wall, wherein the at least one slot is made such that when the cassette is inserted into said slot, said at least one open side is closed substantially by a wall of the slot.
 30. Method according to claim 28, wherein a slot is provided on either side of the heat conducting space, wherein in each slot at least one cassette is provided, water conducting channel parts in the cassettes being interconnected.
 31. Method according to claim 28, wherein a further cassette is inserted into the heat conducting space, said further cassette provided with at least one gas flow channel.
 32. Heating apparatus comprising a heat exchanger according to claim
 1. 33. Heating apparatus comprising a heat exchanger made with a method according to claim
 28. 